The present invention relates to a method for protection against overheating of electromagnetic actuators for actuation of intake and exhaust valves in internal-combustion engines.
As is known, propulsion units are currently at an experimental stage, in which the actuation of the intake and exhaust valves is controlled by means of use of actuators of an electromagnetic type, which replace the purely mechanical distribution systems (cam shafts).
In particular, these actuators comprise a pair of electromagnets disposed on opposite sides of a mobile ferromagnetic element, which is connected to a respective intake or exhaust valve, and is maintained in a position of rest by means of resilient elements (for example a spring and/or a torsion bar). The mobile ferromagnetic element is actuated by means of application of a force generated by distributing suitable currents to the electromagnets, such that the element is made to abut alternately one or the other of the electromagnets themselves, so as to move the corresponding valve between the positions of closure and maximum opening, according to required times and paths. By this means, it is possible to actuate the valves according to optimum raising conditions in all operative conditions of the engine, thus improving substantially the overall performance.
However, in the aforementioned electromagnetic actuators, a serious problem can arise when particularly high currents are distributed. In fact, as a result of, for example, a temporary or permanent malfunctioning, the currents which are supplied to the actuators can assume values which are substantially higher than those planned for the normal functioning conditions. In these cases, the power absorbed can cause sudden overheating of the windings of the electromagnets, and damage them in a few milliseconds in a manner which can even be irreparable. In addition, breakage of the windings makes it impossible to control opening and closure of the valves, and consequently makes the propulsion unit unusable until maintenance intervention is carried out, to replace the faulty actuator(s). In addition, if the cause of the overheating is not correctly determined and eliminated, a high risk of further faults persists.
The object of the present invention is to provide a method for protection against overheating, which makes it possible to overcome the disadvantages described, and which, in particular, makes it possible to reduce the risk of breakage of the windings of the electromagnets.
According to the present invention, a method is provided for protection against overheating of electromagnetic actuators for actuation of intake and exhaust valves in internal-combustion engines, in which an actuator of an engine is connected to a respective intake or exhaust valve, and comprises a mobile unit which is actuated magnetically, in order to control the movement of the said valve, and a first and a second electromagnet, which are disposed on opposite sides of the said mobile unit; the said actuator also being connected to a control unit, via piloting means which supply at least one current, and to current-measuring means; the said current-measuring means supplying to the said control unit measured values of the said at least one current;
the method being characterised in that it comprises the steps of:
a) estimating for each of the said first and second electromagnets, a temperature value which is updated on the basis of a present temperature value and of the said measured values of the said at least one current;
b) checking whether the said updated temperature value is lower than a first threshold; and
c) implementing protective action, if the updated temperature value is higher than the said first threshold.